1. Technical Field
The present invention relates to a gas spring shock absorber.
2. Related Art
Disclosed is a shock absorber which is configured such that a first end of a circular cylindrical inner tube is fixed to a first end fixation portion in a sealed manner, a second end of a circular cylindrical outer tube is fixed to a second end fixation portion in a sealed manner, a second end of the inner tube is inserted into the outer tube via a first end opening of the circular cylindrical outer tube, the inner tube and the outer tube can move relative to each other along the center axis thereof in a state where air-tight sealing between an outer circumferential surface of the inner tube and an inner circumferential surface of the outer tube is formed, a circular cylinder and a circular cylindrical rod are provided inside of the outer tube and the inner tube, a first end of the rod is fixed to the first end fixation portion in such a way that a first end opening of the rod is sealed, a second end of the cylinder is fixed to the second end fixation portion in such a way that a second end opening of the cylinder is sealed, a second end of the rod is inserted into the cylinder via a rod through hole of a rod guide provided at a first end opening of the cylinder, and a piston is provided on a second end portion of the rod which is inserted into the cylinder (for example, refer to JP-A-2013-228089 and the like).
The interior of the shock absorber is divided into three chambers: an inner chamber as a first gas spring chamber that is formed as a sealed space surrounded by the piston, the second end fixation portion, and an inner circumferential surface of the cylinder between the piston and the second end fixation portion; an outer chamber as a second gas spring chamber that is formed as a sealed space surrounded by an outer circumferential surface of the rod, the first end fixation portion, the inner circumferential surfaces of the inner tube and the outer tube, the second end fixation portion, and an outer circumferential surface of the cylinder; and a balance chamber as a third gas spring chamber that is formed as a sealed space surrounded by the piston, the rod guide, and the inner circumferential surface of the cylinder between the piston and the rod guide.
This shock absorber includes a piston lip packing which is provided so as to maintain air-tight sealing between an outer circumferential surface of the piston and the inner circumferential surface of the cylinder such that air-tight sealing between the balance chamber and the inner chamber that are adjacent to each other is maintained, and a rod lip packing which is provided so as to maintain air-tight sealing between the rod through hole of the rod guide and the outer circumferential surface of the rod such that air-tight sealing between the balance chamber and the outer chamber that are adjacent to each other is maintained.
In this shock absorber, in a compression operation in which the first end fixation portion and the second end fixation portion move in such a way as to approach each other, volumes of the inner chamber and the outer chamber are reduced, gas in the inner chamber and the outer chamber is compressed, and thus a gas spring is formed to generate a reaction force that biases the first end fixation portion and the second end fixation portion to move away from each other. In an extension operation in which the first end fixation portion and the second end fixation portion move in such a way as to move away from each other, since the piston and the guide rod move in such a way as to approach each other, a volume of the balance chamber is reduced, gas in the balance chamber is compressed, and thus a gas spring is formed to generate a reaction force that biases the first end fixation portion and the second end fixation portion to approach each other.
The entirety of each of the rod lip packing and the piston lip packing is formed in an annular shape, and respective sections are formed in a lip shape (or a U shape) as illustrated in FIGS. 7 and 8. For this reason, the rod lip packing and the piston lip packing are referred to as a lip packing (or U packing) P. A lip portion positioned on an inner circumference of an annulus of the lip packing P is referred to as an inner circumferential lip IU, and a lip portion positioned on an outer circumference of the annulus is referred to as an outer circumferential lip OU. An inner circumferential surface PF of the inner circumferential lip IU includes an apex portion that protrudes toward a center axis of the annulus, and an inner circumferential surface portion forming the apex portion constitutes a minimum-diameter inner circumferential edge PE, which is a line shape. An outer circumferential surface PG of the outer circumferential lip OU includes an apex portion that protrudes in a direction away from the center axis of the annulus, and an outer circumferential portion forming the apex portion constitutes a maximum-diameter outer circumferential edge PD, which is a line shape.
With regard to the rod lip packing, as illustrated in FIG. 9, a rod lip packing RP is mounted in a packing mounting groove PH provided on an inner circumferential surface of a rod guide RG, a rod R passes through an inner circumferential hole of an annulus of the rod lip packing RP, and an inner circumferential surface (a surface close to the center axis of the annulus) PF of an inner circumferential lip IU of the rod lip packing RP comes into contact with an outer circumferential surface RF of the rod R. An inner circumferential surface PF of an inner circumferential lip IU includes an apex portion that protrudes toward a center axis of an annulus, and the inner circumferential surface portion forming the apex portion constitutes a minimum-diameter inner circumferential edge PE, which is a line shape. That is, as illustrated in FIG. 8, a section of the minimum-diameter inner circumferential edge PE has an angled shape (edge shape).
Accordingly, as illustrated in FIG. 9, when fluid pressure is applied to a region between the inner circumferential lip IU and the outer circumferential lip OU of the rod lip packing RP mounted in the packing mounting groove PH of the rod guide RG, and thus the inner circumferential surface PF of the inner circumferential lip IU comes into contact with the outer circumferential surface RF of the rod R, a contact surface pressure PM between the minimum-diameter inner circumferential edge PE in an angled shape of the inner circumferential surface PF of the inner circumferential lip IU and the outer circumferential surface RF of the rod R is maximized, and thus sealing performance is maintained. Similarly, with regard to the piston lip packing, the piston lip packing is mounted in a packing mounting portion provided on an outer circumferential surface of the piston, an outer circumferential surface (a surface far from the center axis of the annulus) PG of the outer circumferential lip of the piston lip packing comes into contact with an inner circumferential surface of the cylinder. An outer circumferential surface PG of an outer circumferential lip OU includes an apex portion that protrudes in the direction away from the center axis of the annulus, and an outer circumferential portion forming the apex portion constitutes a maximum-diameter outer circumferential edge PD, which is a line shape. That is, as illustrated in FIG. 8, a section of the maximum-diameter outer circumferential edge PD has an angled shape (edge shape).
Accordingly, when the fluid pressure is applied to a region between the outer circumferential lip OU and the inner circumferential lip IU of the piston lip packing mounted in the packing mounting portion of the piston, and thus an outer circumferential surface PG of an outer circumferential lip OU comes into contact with the inner circumferential surface of the cylinder, a contact surface pressure between the maximum-diameter outer circumferential edge PD in an angle shape of the outer circumferential surface PG of the outer circumferential lip OU and the inner circumferential surface of the cylinder is maximized, and thus sealing performance is maintained. Note that compression ratio adjustment oil is sealed in the inner chamber and the outer chamber, and a small amount of oil for forming a sliding oil film is sealed in the balance chamber.
And, as the related art, please also see JP-A-2013-228089.